My own earlier U.S. Pat. No. 4,474,335, issued Oct. 2, 1984 and entitled "Apparatus for Centrifugal Pulp Wood and Wood Chip Grinding" discloses the basic centrifugal grinder. The grinder incorporates an internal grinding surface in the shape of a surface of revolution, with a rotor mounted coaxially within the grinding surface. The rotor has a central cavity which can receive pulp wood or wood chips, and means defining at least one pocket through which material in the central cavity can pass to and contact the grinding surface. A prime mover rotates the rotor with respect to the stationary internal grinding surface.
The centrifugal grinder described in my earlier U.S. Pat. No. 4,474,335 works very satisfactorily. However, with some materials, too many rejects (chip ends and fibre bundles) are produced, and it is desirable to improve the design in such a way as to eliminate or reduce the number of rejects.